1. Field of the Invention
The present invention relates to a technique which prevents deterioration of the lighting characteristic of a discharge lamp from being caused by a variation in supply voltage, thereby ensuring smooth lighting of the discharge lamp.
2. Description of the Related Art
A known lighting circuit for discharge lamps including a metal halide lamp comprises, for example, a DC power supply circuit, which boosts the input voltage from a DC power supply to a predetermined voltage, a DC-AC converter, which converts the DC voltage output from the DC power supply circuit to an AC voltage and supplies the latter voltage to a discharge lamp, and an igniter circuit which generates a high-voltage ignition pulse at the time of igniting the discharge lamp.
The conventional lighting circuit however has such a shortcoming that when the supply voltage varies (e.g., when the supply voltage falls abnormally), the lighting characteristic of a discharge lamp is so deteriorated as to make it difficult to light the discharge lamp.
Accordingly, it is an object of the present invention to permit a discharge lamp to have an excellent lighting characteristic even when the supply voltage varies.